Most people end up with theoretical answer : 3 – Manpower, Material & Equipments which is traditional way of planning a project but not professional.
The picture attached shows 7 types of resources.
Mis-management or non-availability of any of these seven types of resources can lead to failure of project(s).
Some high-level thinkers in the capacity of Project Managers consider “Motivation” as a transparent resource and constantly work on it throughout the duration of the project.
No wonder, they succeed.